T2 display has better contrast, higher reflectivity and warm white color. T1 screen gives colour what is perceived as "gray".
If this is the result of changes in technology, "the ink", or the transmission spectrum of the glass, it does not matter. There is a fact, and this is important.

The improvement of the power supply circuit screen (and perhaps the best of its software configuration) gives a significant effect to reduce the visibility of artifacts: the T1 (left) screen and the T2 on the right with the same book...

thanks for the info, its nice to see a comparison between the screens.

Actually, both look the same to me. I had a PRS505 and i still found the screen to look really nice. To me, the most important thing would be for the screen to look as white as possible, to make it feel like a real book. The artifacts, refresh rate and resolution is irrelevant to me. I never complained about those while reading a printed book, hahaha

I'm not totally convinced of this as I had to get a replacement T1 about a month ago and the very first thing I noticed was the screen was considerably whiter and just better than my old one.

Based on that I doubt theres any difference between the newer T1's and the T2 screen hardware wise at least in recent batches, but I acknowledge software wise the T2 probably does have a few more tricks to help the display.

Maybe there was a change in the T1 screens at some stage of production, or some are just different to others, as my T1 does not show the artifacts shown in the photo at all?

To the eye anyway, it may be different in an image taken with some or all digital cameras due to their sensor frequency sensitivity differing from the eye but if so that is of no relevance to the intended use of the reader.